There must be something really wrong with your truck. My Ram gets 30mpg towing my 5er if I slow down to 80mph or so.....
Now that I think about it, maybe it was around 10mpg at 65, I get a little confused sometimes. That said, was your decreased mileage during the heatwave? Things I've noticed over the years that have a significant impact on fuel mileage are the normal speed, weight, wind etc. I've also noticed that fuel blend and temperature can make a noticeable impact. Towing at 90 to 100 plus degrees tends to have a significant negative impact on my truck.
